1. Field of the Invention
The present invention relates to a method and an apparatus for producing single face corrugated web by adhering a liner web to a medium web corrugated by causing the same to pass through the first corrugating roll and the second corrugating roll, on the outer circumference of which corrugated flutes are formed.
2. Description of the Related Art
An apparatus (so-called single facer) for producing single face corrugated web having a liner web adhered to corrugation crests of a medium web formed to be corrugated is such that the first corrugating roll and second corrugating roll, the outer circumferences of which are have corrugated flutes, are disposed in an up and down relationship so as to be rotatable while they are being engaged at the abovementioned flutes, and a pressure roll is pressure-contacted to the second corrugating roll via the abovementioned medium web and liner web. That is, the medium web is supplied between the first corrugating roll and the second corrugating roll and is provided with appointed corrugated flutes while passing between both rolls. Starch-based glue is coated onto the corrugation crests, by a gluing roller secured to a gluing mechanism. Furthermore, a liner web is supplied from the opposite side of the medium web via the pressure roll, wherein the abovementioned liner web is pressure-contacted to the crests of the medium web and adhered to the medium web between the abovementioned pressure roll and the second corrugating roll, thereby producing a single face corrugated web.
A pressure roll used for a single face corrugated web producing apparatus consists of a metal roll of a large diameter, and the abovementioned roller is opposite to the second corrugating roll with a clearance retained therebetween. And by giving appointed nipping pressure to a medium web and liner web passing between the second corrugating roll and the pressure roll, both of them are adhered to each other at the corrugation crests of the medium web, to which glue is coated. In this case, since flutes consisting of a crest and a trough in continuation are formed at an appointed pitch on the outer circumference of the second corrugating roll, the center of rotation of both rolls slightly changes when the roll pressure-contacting position is made transient from a crest to a trough or from a trough to a crest. As a result of cyclic proximity and separation of the center of rotation of both rolls along with the rotation of both rolls, great vibrations and high noise are generated when producing single face corrugated web, whereby the factory environment is excessively worsened. Furthermore, the crests of the second corrugating roll are cyclically brought into contact with the surface of a pressure roll, resulting from cyclic proximity and separation of the rotation center of both rolls with impacting generated (so-called hammering phenomena occur). Therefore, such a problem arises, by which press lines (so-called press marks) are given to the liner weburface of single face corrugated web produced, in the lateral direction at a pitch of the crests of the second corrugating roll, resulting in a lowering of the commodity value.
Each of the abovementioned various problems results due to the nipping pressure being necessarily set to a greater level since, in a conventional apparatus for producing single face corrugated web, the medium web and liner web are nipped at only one point where the second corrugating roll and pressure roll are opposed to each other. Therefore, as a means to cope with this, such a proposal was made, in which a plurality of pressure rolls are disposed with a spacing therebetween in the circumferential direction of the second corrugating roll, the nipping pressure is set to a smaller value at each of the pressure rolls so that a greater nipping pressure is not given to the medium web and liner web, thereby press marks attached to single face corrugated web are suppressed. Furthermore, such a proposal was made, in which an endless belt is disposed so as to freely travel along the outer circumference of the second corrugating roll, whereby the medium web and liner web are caused to be brought into facial contact with the second corrugating roll in order to suppress generation of vibration, noise or press marks.
However, in any one of the abovementioned countermeasures, since the medium web and liner web are pressure-contacted to the second corrugating roll by a mechanical pressing means, it is impossible to completely eliminate press marks. Furthermore, since the respective pressure rolls are pressed with appointed nipping pressure in a case where a plurality of pressure rolls are used, it is unavoidable for the abovementioned hammering phenomena to be generated in each pressure roll, and a small vibration and noise are generated at each of the pressure rolls, wherein they are multiplied and cause a new problem from which great vibrations and high level noise result. Furthermore, in a case where an endless belt is used, the belt is worn out in time, and it is necessary to replace it periodically. It is pointed out that such a fault arises, by which the running cost is increased. And there is a shortcoming where a "shining" is produced at the liner webide since the endless belt is brought into contact with the liner web.